Many of the automobiles being produced today are equipped with a hydraulic brake system including an anti-lock brake subsystem for assuring that the vehicle wheels do not lock up during sudden applications of the brake. The anti-lock brake system (ABS) is considered by many to be the most significant improvement in vehicle safety within the last decade and it is presently being offered as standard equipment in many vehicles.
Most types of ABS include a singular hydraulic control unit, usually in the form of an aluminum block, in which there is incorporated all of the componentry necessary to provide the anti-lock braking function to the braking system. This includes solenoid actuated isolation valves for isolating a particular wheel brake from braking force exerted through the brake pedal and master cylinder. It also includes solenoid actuated hold/dump valves which are opened to relieve braking pressure at each of the wheel brakes thereby allowing the brake to relax its hold on the wheel. It further includes several low pressure accumulators and a pump for providing supplemental brake pressure to the wheels during the period of controlled braking.
All of this componentry is located in a single control unit, which is typically an aluminum block bored as required to receive the components and to provide fluid communication between the valves, accumulators and pump to complete the hydraulic circuitry. Consequently, the control unit can be of considerable size. For weight reasons, and perhaps more importantly for packaging reasons, it is desirable to maintain this size to an absolute minimum. Heretofore, a substantial amount of space has been required for the block because of the manner in which the solenoid actuated isolation valves and hold/dump valves are secured to the block as well as the manner in which the solenoid part of the valves mates with the electrical control portion of the control unit.
For example, as shown in U.S. Pat. No. 4,828,335, assigned to the assignee of the present invention, each of the isolation valves, dump valves, and accumulators are provided with an externally threaded portion for cooperation with the internally threaded bores of the control unit. For assistance in threading the components into the control unit, the isolation valves, dump valves, and accumulators each include a head having a radially enlarged flange shaped to receive a socket wrench or the like. Thus, the spacing of one valve from the other must be sufficient to accommodate the radial extent of the flange and reception of the socket wrench for the valve's installation into the control unit. This in turn increases the surface area required for the wall of the control unit from which the valves extend, and consequently the overall size of the control unit is increased.
Another factor contributing to the size of the control unit is the fact that the steel casing adapted to slide over the solenoid sleeve and associated coil has heretofore been constructed to be secured to the valve body prior to its installation in the control unit and prior to the electrical control module being fitted over the solenoid sleeves as part of the final assembly process. As shown in the above-referenced U.S. Patent, the casing can be crimped to the valve body portion. It is also known to eliminate the crimping operation and allow the casing to be slip fit over the outer body portion of the valve, either singly or as a part of the electrical control module, since in either case the casing will be in physical contact with the flux ring portion of the valve body.
It is also known to eliminate the socket wrench driving construction of the valve body head to include two diametrically opposed pin holes on the outboard side of the flux ring portion of the valve body thereby allowing the use of a spanner wrench to drive the threaded valve body home within the control unit.